Optical system and optical apparatus

ABSTRACT

An image display apparatus which enables observation of a clear image at a wide field angle with substantially no reduction in the brightness of the observation image, and which is extremely small in size and light in weight and hence unlikely to cause the observer to be fatigued. The image display apparatus includes an image display device (6) for displaying an image, and an ocular optical system (7) for projecting the image displayed by the image display device (6) and for leading the projected image to an observer&#39;s eyeball (1). The ocular optical system (7) has at least three surfaces, and a space formed by the at least three surfaces is filled with a medium having a refractive index larger than 1. The at least three surfaces are, in the order from the observer&#39;s eyeball (1) toward the image display device (6), a first surface (3) which is a refracting surface, a second surface (4) which is decentered or tilted with respect to an observer&#39;s visual axis (2) and serves as both an internally reflecting surface and a refracting surface, and a third surface (5) which is a reflecting surface of positive power facing the second surface (4). Internal reflection at the second surface (4) is total reflection.

This is a division of Application Ser. No. 08/697,059, filed Aug. 20,1996 now U.S. Pat. No. 5,812,323.

BACKGROUND OF THE INVENTION

The present invention relates to an image display apparatus and, moreparticularly, to a head- or face-mounted image display apparatus thatcan be retained on the observer's head or face.

As an example of conventional head- or face-mounted image displayapparatus, an image display apparatus disclosed in Japanese PatentApplication Unexamined Publication (KOKAI) No. 3-101709 (1991) is known.FIG. 14(a) shows the entire optical system of the conventional imagedisplay apparatus, and FIG. 14(b) shows a part of an ocular opticalsystem used in the image display apparatus. As illustrated in thesefigures, in the conventional image display apparatus, an image that isdisplayed by an image display device is transmitted as an aerial imageby a relay optical system including a positive lens, and the aerialimage is projected into an observer's eyeball as an enlarged image by anocular optical system formed from a concave reflecting mirror.

U.S. Pat. No. 4,669,810 discloses another type of conventional imagedisplay apparatus. In this apparatus, as shown in FIG. 15, an image of aCRT is transmitted through a relay optical system to form anintermediate image, and the image is projected into an observer's eye bya combination of a reflection holographic element and a combiner havinga hologram surface.

Japanese Patent Application Unexamined Publication (KOKAI) No. 62-214782(1987) discloses another type of conventional image display apparatus.As shown in FIGS. 16(a) and 16(b), the conventional image displayapparatus is designed to enable an image of an image display device tobe directly observed as an enlarged image through an ocular lens.

U.S. Pat. No. 4,026,641 discloses another type of conventional imagedisplay apparatus. In the conventional image display apparatus, as shownin FIG. 17, an image of an image display device is transferred to acurved object surface by an image transfer device, and the imagetransferred to the object surface is projected in the air by a toricreflector.

U.S. Reissued Pat. No. 27,356 discloses another type of conventionalimage display apparatus. As shown in FIG. 18, the apparatus is an ocularoptical system designed to project an object surface onto an exit pupilby a semitransparent concave mirror and a semitransparent plane mirror.

In image display apparatuses of the type wherein an image of an imagedisplay device is relayed, as shown in FIGS. 14(a), 14(b) and 15,however, several lenses must be used as a relay optical system inaddition to an ocular optical system, regardless of the type of ocularoptical system. Consequently, the optical path length increases, and theoptical system increases in both size and weight.

In a case where only the ocular optical system shown in FIG. 14(a) isused, as shown in FIG. 14(b), positive power resides in only thereflecting surface that has a concave surface directed toward theobserver. Therefore, large negative field curvature is produced as shownby reference character P1 in the figure.

In a layout such as that shown in FIG. 16, the amount to which theapparatus projects from the observer's face undesirably increases.Further, because an image display device and an illumination opticalsystem are attached to the projecting portion of the apparatus, theapparatus becomes increasingly large in size and heavy in weight.

Because a head-mounted image display apparatus is fitted to the humanbody, particularly the head, if the amount to which the apparatusprojects from the user's face is large, the distance from the supportingpoint on the head to the center of gravity of the apparatus is long.Consequently, the weight of the apparatus is imbalanced when theapparatus is fitted to the observer's head. Further, when the observermoves or turns with the apparatus fitted to his/her head, the apparatusmay collide with something.

That is, it is important for a head-mounted image display apparatus tobe small in size and light in weight. An essential factor in determiningthe size and weight of the apparatus is the arrangement of the opticalsystem.

However, if an ordinary magnifier alone is used as an ocular opticalsystem, exceedingly large aberrations are produced, and there is nodevice for correcting them. Even if spherical aberration can becorrected to a certain extent by forming the configuration of theconcave surface of the magnifier into an aspherical surface, otheraberrations such as coma and field curvature remain. Therefore, if thefield angle for observation is increased, the image display apparatusbecomes impractical. Alternatively, if a concave mirror alone is used asan ocular optical system, it is necessary to use not only ordinaryoptical elements (lens and mirror) but also a device for correctingfield curvature by an image transfer device (fiber plate) having asurface which is curved in conformity to the field curvature produced,as shown in FIG. 17.

In a coaxial ocular optical system in which an object surface isprojected onto an observer's pupil by using a semitransparent concavemirror and a semitransparent plane mirror, as shown in FIG. 18, becausetwo semitransparent surfaces are used, the brightness of the image isreduced to as low a level as 1/16, even in the case of a theoreticalvalue. Further, because field curvature that is produced by thesemitransparent concave mirror is corrected by curving the objectsurface itself, it is difficult to use a flat display, e.g. an LCD(Liquid Crystal Display), as an image display device.

SUMMARY OF THE INVENTION

In view of the above-described problems of the conventional techniques,an object of the present invention is to provide an image displayapparatus which enables observation of a clear image at a wide fieldangle with substantially no reduction in the brightness of theobservation image, and which is extremely small in size and light inweight and hence unlikely to cause the observer to be fatigued.

To attain the above-described object, the present invention provides animage display apparatus which includes an image display device fordisplaying an image, and an ocular optical system for projecting theimage displayed by the image display device and for leading theprojected image to an observer's eyeball. The ocular optical system hasat least three surfaces, and a space formed by the at least threesurfaces is filled with a medium having a refractive index largerthan 1. The at least three surfaces are, in the order from theobserver's eyeball toward the image display device, a first surfacewhich is a refracting surface, a second surface which is decentered ortilted with respect to an observer's visual axis and serves as both aninternally reflecting surface and a refracting surface, and a thirdsurface which is a reflecting surface of positive power facing thesecond surface. Internal reflection at the second surface is totalreflection.

In this case, the first surface of the ocular optical system isdesirably tilted or decentered with respect to the observer's visualaxis.

In addition, the present invention provides an image display apparatuswhich includes an image display device for displaying an image, and anocular optical system for projecting the image displayed by the imagedisplay device and for leading the projected image to an observer'seyeball. The ocular optical system has a decentered optical element, andat least one optical surface having a refracting or reflecting action.The decentered optical element and the at least one optical surface aredisposed in an optical path extending from the image display device tothe observer's eyeball. The decentered optical element has at leastthree surfaces, and a space formed by the at least three surfaces isfilled with a medium having a refractive index larger than 1. The atleast three surfaces are, in the order from the observer's eyeballtoward the image display device, a first surface which is a refractingsurface, a second surface which is decentered or tilted with respect toan observer's visual axis and serves as both an internally reflectingsurface and a refracting surface, and a third surface which is a surfaceof positive power facing the second surface. Internal reflection at thesecond surface is total reflection.

The operation of the above-described image display apparatus accordingto the present invention will be explained below. The followingexplanation will be given on the basis of backward ray tracing in whichlight rays are traced from the observer's pupil position toward theimage display device for the convenience of designing an optical system.

The basic arrangement of the present invention is as follows: An imagedisplay apparatus includes an image display device for displaying animage, and an ocular optical system for projecting the image displayedby the image display device and for leading the projected image to anobserver's eyeball. The ocular optical system has at least threesurfaces, and a space formed by the at least three surfaces is filledwith a medium having a refractive index larger than 1. The at leastthree surfaces are, in the order from the observer's eyeball toward theimage display device, a first surface which is a refracting surface, asecond surface which is decentered or tilted with respect to anobserver's visual axis and serves as both an internally reflectingsurface and a refracting surface, and a third surface which is areflecting surface of positive power facing the second surface. Internalreflection at the second surface is total reflection. In the sequence ofbackward ray tracing from the observer's eyeball side, surface Nos. areserially given to the three surfaces in the order, the first surface,the second surface, the third surface, and the second surface.

The reason for adopting the above-described arrangement is as follows:If the first to third surfaces are optical elements independent of eachother, exceedingly high accuracy is demanded for the angle, distance,etc. when these optical elements are disposed. Consequently, it becomesdifficult to assemble the optical system, and the productivity reduces.The second and third surfaces, which are internal reflecting surfaces ofthe optical element constituting the ocular optical system, produce nochromatic aberration. Refraction at the second surface produces minimalchromatic aberration because the inclination angle of light rays to thesurface is small. Accordingly, chromatic aberration in the ocularoptical system of the present invention occurs at only the firstsurface; it is relatively small as a whole. If an ordinary reflectingmirror is used as the second surface, it is necessary to use ahalf-mirror, which reflects a part of incident light rays and transmitsa part of them, in order to assign reflecting and transmitting actionsto the second surface as in the present invention. However, the use of ahalf-mirror causes the brightness of an image to be observed to reduceto about 1/4 before the image reaches the observer's eyeball. Therefore,the first to third surfaces are integrally formed as one unit, therebyfacilitating the assembly and achieving an improvement in productivity.Further, total reflection is utilized as the internal reflection at thesecond surface, thereby enabling observation of an image which is clearand bright as far as the edges of the image field at a wide field angledespite a compact structure.

Advantageous effects achieved by the above-described arrangement will beexplained below.

First, the refracting action at the first surface makes it possible tominimize the height of extra-axial rays when reflected by the secondsurface. Consequently, it becomes possible to construct the opticalelement in a compact form. In other words, it becomes possible to set awide field angle despite a compact optical element.

Further, the optical system is arranged such that the internalreflection at the second surface satisfies the condition for totalreflection, and the third surface is assigned principal positive power,thereby succeeding in preventing the occurrence of comatic aberration atthe third surface.

In general, a concave mirror having strong power produces strongnegative comatic aberration. In the case of a concave mirror decenteredor tilted with respect to the optical axis, the amount of comaticaberration increases as the inclination angle of the concave mirrorbecomes larger. However, it is necessary in order to widen the fieldangle to increase the inclination angle of a reflecting surface whichlies immediately in front of the observer's eyeball because the imagedisplay device and the observer's head would otherwise interfere witheach other. Therefore, the ocular optical system according to thepresent invention is arranged such that the second surface, which is areflecting surface immediately in front of the eyeball, has a largereflection angle to perform total reflection and has no strong power. Onthe other hand, the third surface is given principal positive power, andthe angle of reflection at this concave mirror is reduced. This makes itpossible to minimize comatic aberration due to the decentration.

Further, unlike a conventional arrangement in which an observation imageof an image display device is formed in the air as a real intermediateimage by a relay optical system and the image is projected into anobserver's eyeball as an enlarged image by an ocular optical system, theocular optical system according to the present invention projects animage of an image display device directly into an observer's eyeball asan enlarged image, thereby enabling the observer to view the enlargedimage of the image display device as a virtual image. Accordingly, theoptical system can be constructed with a reduced number of opticalelements.

The first surface of the above-described ocular optical system isdesirably tilted or decentered with respect to the observer's visualaxis. Tilting or decentering the first surface makes it possible tocorrect comatic aberrations asymmetrically introduced into an imagewhich lies closer to the image display device relative to the observer'svisual axis and into an image which lies on the opposite side, and alsopossible to dispose the image display device on a plane which isapproximately perpendicular to the optical axis reflected by the thirdsurface. This is effective when an image display device which isinferior in viewing angle characteristics is used.

The third surface of the ocular optical system is desirably tilted ordecentered with respect to the observer's visual axis. Light raystotally reflected by the second surface are reflected again by the thirdsurface, which is a concave mirror. Because the direction of reflectionat the third surface tilts closer to the image display device than theincident light from the second surface, it is possible to allow thereflected light to emanate forwardly from the second surface and todispose the image display device above the slant surface of the secondsurface. Accordingly, the whole apparatus can be constructed in a thinform. Moreover, with the above-described arrangement, the incident angleof light rays to the second surface reduces. Therefore, it is possibleto minimize chromatic aberration occurring when light rays are refractedby the second surface.

If two of the three surfaces constituting the optical element of theocular optical system have a finite radius of curvature, it becomespossible to correct spherical and comatic aberrations produced by theeccentrically tilted third surface. Thus, it is possible to provide theobserver with a clear observation image having a wide exit pupildiameter and a wide observation field angle.

In a case where two of the three surfaces of the ocular optical systemhave a finite radius of curvature, if the first surface has a finiteradius of curvature in addition to the second surface and it haspositive power, the effect of refraction of light rays by the firstsurface is enhanced. Therefore, the size of the ocular optical systemcan be further reduced. Alternatively, the field angle can be widened.Further, because the height of subordinate rays reduces, it becomespossible to minimize comatic aberrations produced by the second surface,particularly higher-order comatic aberrations.

In a case where the second surface has a finite radius of curvature inaddition to the third surface and it has positive power, it becomes easyto satisfy the condition for total reflection of extra-axial rays at thesecond surface, and it is possible to realize an exceedingly wide fieldangle.

It is useful for aberration correction that any one of the first, secondand third surfaces of the ocular optical system is a decenteredaspherical surface.

Let us define a coordinate system as follows: With the observer's irisposition defined as the origin, the direction of the observer's visualaxis is taken as a Z-axis, where the direction toward the ocular opticalsystem from the origin is defined as a positive direction. The verticaldirection (as viewed from the observer's eyeball) which perpendicularlyintersects the observer's visual axis is taken as a Y-axis, where theupward direction is defined as a position direction. The horizontaldirection (as viewed from the observer's eyeball) which perpendicularlyintersects the observer's visual axis is taken as an X-axis, where theleftward direction is defined as a positive direction. In this case, theabove-described arrangement, in which any one of the first, second andthird surfaces of the ocular optical system is a decentered asphericalsurface, is an important condition for correcting comatic aberrations,particularly higher-order comatic aberrations and coma flare, producedby the second surface decentered in the direction Y or tilted from thevisual axis.

In an image display apparatus that uses an ocular optical system of thetype having a decentered or tilted reflecting surface in front of anobserver's eyeball as in the present invention, light rays are obliquelyincident on the reflecting surface even on the observer's visual axis,causing comatic aberration to occur. The comatic aberration increases asthe inclination angle of the reflecting surface increases. However, theamount of decentration or the angle of inclination must be increased toa certain extent in order to realize a compact and wide-field imagedisplay apparatus because the image display device and the optical pathwould otherwise interfere with each other. Thus, it is difficult toensure an observation image of wide field angle unless the decentrationor the inclination is increased to a certain extent.

Accordingly, as the field angle of an image display apparatus becomeswider and the size thereof becomes smaller, the inclination angle of thereflecting surface becomes larger. As a result, how to correcthigher-order comatic aberrations becomes a serious problem.

To correct such complicated comatic aberrations, a decentered asphericalsurface is used as any one of the first, second and third surfacesconstituting the ocular optical system. By doing so, the power of theoptical system can be made asymmetric with respect to the visual axis.Further, the effect of the aspherical surface can be utilized foroff-axis aberration. Accordingly, it becomes possible to effectivelycorrect comatic aberrations, including axial aberration.

It is important that any one of the first, second and third surfaces ofthe ocular optical system should be an anamorphic surface. That is, anyone of the three surfaces should be a surface in which the radius ofcurvature in the YZ-plane and the curvature radius in the XZ-plane,which perpendicularly intersects the YZ-plane, are different from eachother.

The above is a condition for correcting aberration which occurs becausethe second surface is decentered or tilted with respect to the visualaxis. In general, if a spherical surface is decentered, the curvaturerelative to light rays incident on the surface in the plane of incidenceand that in a plane perpendicularly intersecting the incidence planediffer from each other. Therefore, in an ocular optical system where areflecting surface is disposed in front of an observer's eyeball in sucha manner as to be decentered or tilted with respect to the visual axisas in the present invention, an image on the visual axis lying in thecenter of the observation image is also astigmatically aberrated for thereason stated above. In order to correct the axial astigmatism, it isimportant that any one of the first, second and third surfaces of theocular optical system should be formed so that the curvature radius inthe plane of incidence and that in a plane perpendicularly intersectingthe incidence plane are different from each other.

Assuming that R_(y) is the radius of curvature in the YZ-plane of anyone of the first, second and third surfaces of the ocular opticalsystem, which is an anamorphic surface, and R_(x) is the radius ofcurvature in the XZ-plane of that surface, it is preferable to satisfythe following condition:

    R.sub.y /R.sub.x ≧1                                 (1)

The above expression (1) is a condition for correcting aberrations,particularly axial and other astigmatic aberrations, which occur becausethe second surface is tilted with respect to the visual axis. Ingeneral, as the field angle becomes larger, higher-order astigmaticaberrations appear. In a convex lens system, as the field angle becomeslarger, the meridional image increases in the negative direction,whereas the sagittal image increases in the positive direction. In orderto correct these astigmatic aberrations, it is necessary to arrange theoptical system such that the power in the meridional plane is reduced,whereas the power in the sagittal plane is increased. Accordingly, it ispreferable from the viewpoint of aberration correction that thecurvature radius of at least one anamorphic surface should be increasedin the direction Y and reduced in the direction X.

Further, it is desirable to satisfy the following condition:

    30°<α<70°                              (2)

where α is the angle between the second surface of the ocular opticalsystem and the visual axis.

This is a condition for disposing the ocular optical system and theimage display device of the image display apparatus according to thepresent invention at appropriate positions. If α is not larger than thelower limit of the condition (2), i.e. 30°, light rays after reflectionhave a reflection angle of 90° or more with respect to the visual axis.Consequently, the image-formation positions of the upper and lowerextra-axial rays on the image field are exceedingly separated from eachother, which is not realistic. Conversely, if α is not smaller than theupper limit of the condition (2), i.e. 70°, the reflection angle at thesecond surface becomes exceedingly small, and it becomes impossible tosatisfy the condition for total reflection.

Further, it is important that the display surface of the image displaydevice should be tilted with respect to the visual axis. In a case wherea refracting surface or a reflecting surface which constitutes anoptical element is decentered or tilted, the refraction or reflectionangle of light rays from the pupil at the refracting or reflectingsurface may vary according to the image height, causing the imagesurface to be tilted with respect to the visual axis. In such a case,the inclination of the image surface can be corrected by tilting thedisplay surface of the image display device with respect to the visualaxis.

Incidentally, as the field angle of an image display apparatus widensand the size thereof decreases, the inclination angle of the secondsurface, which is the first reflecting surface, increases, andhigher-order comatic aberrations produced thereby increase. Further,astigmatism that is produced by the inclination of the surface alsoincreases. Accordingly, it may be difficult to satisfactorily correctthese aberrations by only a decentered optical element in which a spaceformed by three surfaces is filled with a medium having a refractiveindex larger than 1, and in which the three surfaces are, in the orderfrom the observer's eyeball toward the image display device, a firstsurface which is a refracting surface, a second surface which isdecentered or tilted with respect to an observer's visual axis andserves as both an internally reflecting surface and a refractingsurface, and a third surface which is a reflecting surface of positivepower facing the second surface, in which internal reflection at thesecond surface is total reflection.

Therefore, at least one optical surface having a refracting orreflecting action is disposed, in addition to the above-describeddecentered optical element, between the observer's eyeball and the imagedisplay device. This enables even more effective correction ofaberrations produced in the ocular optical system.

In the decentered optical element of the present invention, the secondsurface and the internally reflecting surface of the third surface,which is subsequent to the second surface, are reflecting surfaces.Therefore, no chromatic aberration is produced at these surfaces.Further, at the second surface, which lies in close proximity to theimage display device, the principal ray is approximately parallel to theoptical axis. Therefore, the second surface produces minimal chromaticaberration. Consequently, chromatic aberration produced by the firstsurface, which is a refracting surface, is dominant in the ocularoptical system. It should, however, be noted that, when the thirdsurface is a refracting surface, chromatic aberration is also producedby the third surface. In a wide-field optical system such as that in thepresent invention, lateral chromatic aberration appears more markedlythan axial chromatic aberration. That is, it is important to correctlateral chromatic aberration produced by the first surface, and it ispossible to display an image which is clearer and of higher resolutionby correcting the lateral chromatic aberration.

Accordingly, the ocular optical system is preferably arranged such thatthe decentered optical element, together with at least one opticalsurface having a refracting or reflecting action, is disposed betweenthe observer's eyeball and the image display device. By doing so,optical elements constituting the ocular optical system can be composedof two or more different mediums, and it becomes possible to correct thelateral chromatic aberration by virtue of the difference in Abbe'snumber between these mediums.

As has been described above, it is important in the ocular opticalsystem of the present invention to correct chromatic aberration producedby the first surface of the decentered optical element. The chromaticaberration can be corrected by forming the above-described at least oneoptical surface from a surface which produces chromatic aberration whichis approximately equal in quantity but opposite in sign to the chromaticaberration produced by the first surface.

In a case where the above-described at least one optical surface isdisposed between the observer's eyeball and the first surface of thedecentered optical element, and the optical surface has positiverefracting power, the beam diameter at the second surface of thedecentered optical element becomes small, and hence higher-order comaticaberrations reduce. Therefore, it is possible to observe a clear imageas far as the edges of the image display area of the image displaydevice. Further, because a principal ray at the edge of the image isrefracted by the at least one optical surface having positive refractingpower, the height of the ray incident on the decentered optical systemcan be reduced. Therefore, it becomes possible to set a larger fieldangle than in a case where the decentered optical system alone is used.

In a case where the above-described at least one optical surface isdisposed between the first to third surfaces of the decentered opticalelement, the decentered optical element is composed of two differentmediums, as has been described above; this is useful to correctchromatic aberration.

In a case where the above-described at least one optical surface isdisposed between the decentered optical element and the image displaydevice, if the optical surface has negative power, it is possible toreduce the inclination angle of extra-axial principal rays to thedisplay device. This is effective when an image display device which isinferior in viewing angle characteristics at the edges of the imagedisplay area is used.

By decentering the above-described at least one optical surface withrespect to the visual axis, it is possible to correct comaticaberrations asymmetrically introduced into an image which lies closer tothe image display device as viewed from the visual axis and into animage which lies on the opposite side, and also possible to allow theoptical axis to lie approximately perpendicular to a plane on which theimage display device is disposed.

By using a cemented lens to form the above-described at least oneoptical surface, lateral chromatic aberration produced in the decenteredoptical system can be corrected; this is useful to ensure a clearerimage and a wider field angle.

It should be noted that it becomes possible for the observer to see astable observation image by providing a device for positioning both theimage display device and the ocular optical system with respect to theobserver's head.

By allowing both the image display device and the ocular optical systemto be fitted to the observer's head with a supporting device, it becomespossible for the observer to see the observation image in a desiredposture and from a desired direction.

Further, it becomes possible for the observer to see the observationimage with both eyes without fatigue by providing a device forsupporting at least two image display apparatuses as described above ata predetermined spacing. Further, if images with a disparitytherebetween are displayed on the right and left image display surfaces,and these images are observed with both eyes, it is possible to enjoyviewing a stereoscopic image.

Further, if the optical system according to the present invention isarranged to form an image of an object at infinity with the imagedisplay device surface in the ocular optical system defined as an imagesurface, the optical system according to the present invention can beused as an imaging optical system, e.g. a finder optical system for acamera such as that shown in FIG. 12.

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specification.

The invention accordingly comprises the features of construction,combinations of elements, and arrangement of parts which will beexemplified in the construction hereinafter set forth, and the scope ofthe invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an optical ray trace of Example 1 of the imagedisplay apparatus according to the present invention.

FIG. 2 illustrates an optical ray trace of Example 2 of the imagedisplay apparatus according to the present invention.

FIG. 3 illustrates an optical ray trace of Example 3 of the imagedisplay apparatus according to the present invention.

FIG. 4 illustrates an optical ray trace of Example 4 of the imagedisplay apparatus according to the present invention.

FIG. 5 illustrates an optical ray trace of Example 5 of the imagedisplay apparatus according to the present invention.

FIG. 6 illustrates an optical ray trace of Example 6 of the imagedisplay apparatus according to the present invention.

FIG. 7 illustrates an optical ray trace of Example 7 of the imagedisplay apparatus according to the present invention.

FIG. 8 illustrates an optical ray trace of Example 8 of the imagedisplay apparatus according to the present invention.

FIG. 9 illustrates an optical ray trace of Example 9 of the imagedisplay apparatus according to the present invention.

FIG. 10 illustrates an optical ray trace of Example 10 of the imagedisplay apparatus according to the present invention.

FIGS. 11(a) and 11(b) are sectional and perspective views showing ahead-mounted image display apparatus according to the present invention.

FIG. 12 shows an arrangement in which an optical apparatus according tothe present invention is used as an imaging optical system.

FIG. 13 shows an arrangement of an optical system in which an opticalapparatus according to the present invention is used as an imagingoptical system.

FIG. 14(a) and 14(b) show an optical system of a conventional imagedisplay apparatus.

FIG. 15 shows an optical system of another conventional image displayapparatus.

FIGS. 16(a) and 16(b) show an optical system of still anotherconventional image display apparatus.

FIG. 17 shows an optical system of a further conventional image displayapparatus.

FIG. 18 shows an optical system of a still further conventional imagedisplay apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Examples 1 to 10 of the image display apparatus according to the presentinvention will be described below with reference to FIGS. 1 to 10, whichare sectional views of image display apparatuses designed for a singleeye according to Examples 1 to 10.

Constituent parameters of Examples 1 to 10 will be shown later. In thefollowing description, surface Nos. are shown as ordinal numbers inbackward tracing from an observer's pupil position 1 toward an imagedisplay device 6. A coordinate system is defined as follows: As shown inFIG. 1, with the observer's pupil position 1 defined as the origin, thedirection of an observer's visual axis 2 is taken as a Z-axis, where thedirection toward an ocular optical system 7 from the origin is definedas a positive direction. The vertical direction (as viewed from theobserver's eyeball) which perpendicularly intersects the observer'svisual axis 2 is taken as a Y-axis, where the upward direction isdefined as a position direction. The horizontal direction (as viewedfrom the observer's eyeball) which perpendicularly intersects theobserver's visual axis 2 is taken as an X-axis, where the leftwarddirection is defined as a positive direction. That is, the plane of thefigure is defined as a YZ-plane, and a plane which is perpendicular tothe plane of the figure is defined as an XZ-plane. Further, it isassumed that the optical axis is bent in the YZ-plane, which is parallelto the plane of the figure.

In the constituent parameters (shown later), regarding each surface forwhich eccentricities Y and z and tilt angle θ are shown, theeccentricity Y is a distance by which the vertex of the surfacedecenters in the Y-axis direction from the surface No. 1 (pupil position1), which is a reference surface. The eccentricity Z is a distance bywhich the vertex of the surface decenters in the Z-axis direction fromthe surface No. 1. The tilt angle θ is the angle of inclination of thecentral axis of the surface from the Z-axis. In this case, positive θmeans counterclockwise rotation. It should be noted that a surfacewithout indication of eccentricities Y, Z and tilt angle θ is coaxialwith respect to the preceding surface.

Regarding surface separations, the surface separation of the surface No.2 is the distance from the surface No. 1 along the Z-axis direction, anda point on the surface No. 2 that lies on the Z-axis is defined as areference point. A point which decenters from the reference point in thedirection Y by the given eccentricity is the vertex of the surface No.2. Regarding the coaxial portion, the surface separation is the axialdistance from the surface concerned to the next surface. It should benoted that surface separations are shown with the direction of backwardtracing along the optical axis defined as a positive direction.

The non-rotationally symmetric aspherical configuration of each surfacemay be expressed in the coordinate system defining the surface asfollows: ##EQU1## where R_(y) is the paraxial curvature radius of eachsurface in the YZ-plane (the plane of the figure); R_(x) is the paraxialcurvature radius in the XZ-plane; K_(x) is the conical coefficient inthe XZ-plane; K_(y) is the conical coefficient in the YZ-plane; AR andBR are 4th- and 6th-order aspherical coefficients, respectively, whichare rotationally symmetric with respect to the Z-axis; and AP and BP are4th- and 6th-order aspherical coefficients, respectively, which arerotationally asymmetric with respect to the Z-axis.

It should be noted that the refractive index of the medium between apair of surfaces is expressed by the refractive index for the spectrald-line. Lengths are given in millimeters.

The following examples are all image display apparatuses for the righteye. An image display apparatus for the left eye can be realized bydisposing the constituent optical elements of each example insymmetrical relation to the apparatus for the right eye with respect tothe YZ-plane.

In an actual apparatus, needless to say, the direction in which theoptical axis is bent by the ocular optical system may be any of theupward, downward and sideward directions of the observer.

In each sectional view, reference numeral 1 denotes an observer's pupilposition, 2 an observer's visual axis, 3 a first surface of an ocularoptical system, 4 a second surface of the ocular optical system, 5 athird surface of the ocular optical system, and 6 an image displaydevice. Reference numeral 7 denotes the ocular optical system having thefirst, second and third surfaces 3, 4 and 5. Reference numeral 8 denotesa decentered optical element, and reference numerals 9 and 9' denoteoptical surfaces.

The actual path of light rays in each example is as follows: In Example1, for instance, a bundle of light rays emitted from the image displaydevice 6 enters the ocular optical system 7 while being refracted by thesecond surface 4 of the ocular optical system 7. The incident ray bundleis internally reflected by the third surface 5 and totally reflected bythe second surface 4. Then, the ray bundle is incident on the firstsurface 3 and refracted thereby so as to be projected into theobserver's eyeball with the observer's iris position or eyeball rollingcenter as the exit pupil 1.

EXAMPLE 1

In this example, as shown in the sectional view of FIG. 1, thehorizontal field angle is 48°, while the vertical field angle is 36.9°,and the pupil diameter is 4 millimeters. In the constituent parameters(shown later), the surface Nos. 2 and 4 are anamorphic asphericalsurfaces, and the surfaces Nos. 3 and 5 are plane surfaces.

EXAMPLE 2

In this example, as shown in the sectional view of FIG. 2, thehorizontal field angle is 30°, while the vertical field angle is 22.7°,and the pupil diameter is 12 millimeters. In the constituent parameters(shown later), the surface Nos. 2 to 5 are spherical surfaces.

EXAMPLE 3

In this example, as shown in the sectional view of FIG. 3, thehorizontal field angle is 55°, while the vertical field angle is 42.7°,and the pupil diameter is 4 millimeters. In the constituent parameters(shown later), the surface Nos. 2 to 5 are anamorphic asphericalsurfaces.

EXAMPLE 4

In this example, as shown in the sectional view of FIG. 4, thehorizontal field angle is 40°, while the vertical field angle is 30.5°,and the pupil diameter is 4 millimeters. In the constituent parameters(shown later), the surface Nos. 2, 4, 5, 7 and 8 are spherical surfaces,and the surface Nos. 3, 6 and 9 are anamorphic aspherical surfaces.Optical surfaces are defined by the surface Nos. 5 to 7 and decenteredwith respect to the visual axis 2.

EXAMPLE 5

In this example, as shown in the sectional view of FIG. 5, thehorizontal field angle is 40°, while the vertical field angle is 30.5°,and the pupil diameter is 8 millimeters. In the constituent parameters(shown later), the surface Nos. 4 and 6 are spherical surfaces, and thesurface Nos. 2, 3, 5 and 7 are anamorphic aspherical surfaces. Opticalsurfaces are defined by the surface Nos. 4 and 6 and decentered withrespect to the visual axis 2.

EXAMPLE 6

In this example, as shown in the sectional view of FIG. 6, thehorizontal field angle is 48°, while the vertical field angle is 36.9°,and the pupil diameter is 4 millimeters. In the constituent parameters(shown later), the surface Nos. 2, 4 and 6 are spherical surfaces, andthe surface Nos. 3, 5 and 7 are anamorphic aspherical surfaces. Opticalsurfaces are defined by the surface Nos. 4 and 6 and decentered withrespect to the visual axis 2.

EXAMPLE 7

In this example, as shown in the sectional view of FIG. 7, thehorizontal field angle is 50°, while the vertical field angle is 38.5°,and the pupil diameter is 4 millimeters. In the constituent parameters(shown later), the surface Nos. 2 and 3 are spherical surfaces, and thesurface Nos. 4, 5 and 6 are anamorphic aspherical surfaces. An opticalsurface is defined by the surface No. 3 and decentered with respect tothe visual axis 2.

EXAMPLE 8

In this example, as shown in the sectional view of FIG. 8, thehorizontal field angle is 50°, while the vertical field angle is 38.5°,and the pupil diameter is 4 millimeters. In the constituent parameters(shown later), the surface Nos. 2, 3 and 4 are spherical surfaces, andthe surface Nos. 5, 6 and 7 are anamorphic aspherical surfaces. Opticalsurfaces are formed by a positive lens defined by the surface Nos. 2 and3. The positive lens is disposed between the decentered optical element8 and the observer's eyeball 1 in such a manner as to be decentered withrespect to the visual axis 2.

EXAMPLE 9

In this example, as shown in the sectional view of FIG. 9, thehorizontal field angle is 52°, while the vertical field angle is 40.2°,and the pupil diameter is 4 millimeters. In the constituent parameters(shown later), the surface Nos. 2, 3, 5 and 7 are spherical surfaces,and the surface Nos. 4, 6 and 8 are anamorphic aspherical surfaces.Optical surfaces are defined by the surface Nos. 3, 5 and 7 anddecentered with respect to the visual axis 2.

EXAMPLE 10

In this example, as shown in the sectional view of FIG. 10, thehorizontal field angle is 40°, while the vertical field angle is 30.5°,and the pupil diameter is 10 millimeters. In the constituent parameters(shown later), the surface Nos. 2 to 7 are spherical surfaces. Opticalsurfaces are defined by the surface Nos. 6 and 7 and decentered withrespect to the visual axis 2. In this example, the optical surfaces areformed as a single lens disposed between the image display device 6 andthe decentered optical element 8. However, the single lens may bereplaced by a cemented lens.

Constituent parameters of the above-described Examples 1 to 10 are asfollows:

    __________________________________________________________________________                           Refractive    Surface Radius of                    Surface                           index    Abbe's No.    No.     curvature                    separation                           (Eccentricity)                                    (Tilt angle)    __________________________________________________________________________    Example 1    1       ∞(pupil)                    30.042    2     R.sub.y            81.816         1.4870   70.40          R.sub.x            44.764       Y -0.759 θ                                    3.44°          K.sub.y            2.586634          K.sub.x            -.6206961          AR            -1.12255 × 10.sup.-6          BR            7.46253 × 10.sup.-10          AP            0.845407          BP            0.790479    3       ∞        1.4870   70.40                         Y 14.068 θ                                    51.23°                         Z 32.634    4     R.sub.y            111.203        1.4870   70.40          R.sub.x            125.686      Y -13.468                                  θ                                    62.15°          K.sub.y            -0.399652    Z 29.862          K.sub.x            2.873441          AR            4.34333 × 10.sup.-8          BR            2.28072 × 10.sup.-12          AP            -1.7788          BP            0.946485    5       ∞      Y 14.068 θ                                    51.23°                         Z 32.634    6       (display device)                         Y 1.410  θ                                    71.51°                         Z 75.077    (1)  R.sub.y /R.sub.x = 1.828    (2) α = 38.77°    Example 2    1       ∞(pupil)                    28.912    2       149.553        1.4870   70.40                         Y -21.668                                  θ                                    1.50°    3       941.611        1.4870   70.40                         Y -0.102 θ                                    47.77°                         Z 47.230    4       149.800        1.4870   70.40                         Y -18.949                                  θ                                    70.67°                         Z 33.163    5       941.611      Y -0.102 θ                                    47.77°                         Z 47.230    6       (display device)                         Y 24.665 θ                                    73.70°                         Z 78.142    (1)  R.sub.y 2/R.sub.x 2 = 1    (2) α = 42.23°    Example 3    1       ∞(pupil)                    21.322    2     R.sub.y            143.843        1.4922   57.50          R.sub.x            29.666       Y -22.583                                  θ                                    -0.80°          K.sub.y            -10.678912          K.sub.x            -4.18065          AR            -1.35839 × 10.sup.-8          BR            -5.14664 × 10.sup.-10          AP            8.40197          BP            -0.552947    3     R.sub.y            -184.192       1.4922   57.50          R.sub.x            -456.655     Y 5.564  θ                                    53.46°          K.sub.y            -2.917159    Z 39.811          K.sub.x            -5.539583          AR            -8.14666 × 10.sup.-8          BR            2.56706 × 10.sup.-12          AP            0.356072          BP            -0.517181    4     R.sub.y            70.860         1.4922   57.50          R.sub.x            166.306      Y -13.573                                  θ                                    60.00°          K.sub.y            -8.773779    Z 22.549          K.sub.x            -1.385752          AR            3.69119 × 10.sup.-7          BR            -1.17043 × 10.sup.-12          AP            -1.26444          BP            1.53099    5     R.sub.y            -184.192     Y 5.564  θ                                    53.46°          R.sub.x            -456.655     Z 39.811          K.sub.y            -2.917159          K.sub.x            -5.539583          AR            -8.14666 × 10.sup.-8          BR            2.56706 × 10.sup.-12          AP            0.356072          BP            -0.517181    6       (display device)                         Y -6.789 θ                                    68.00°                         Z 68.196    (1)  R.sub.y /R.sub.x = 4.849    (2) α = 36.54°    Example 4    1       ∞(pupil)                    29.185    2       102.985        1.5092   68.07                         Y 0.923  θ                                    -2.81°    3     R.sub.y            491.360        1.5092   68.07          R.sub.x            ∞      Y 9.366  θ                                    49.18°          K.sub.y            -23.545228   Z 33.561          K.sub.x            0.000000          AR            -3.12497 × 10.sup.-10          BR            3.17327 × 10.sup.-12          AP            -3.99521          BP            -0.577359    4       111.602      Y -18.553                                  θ                                    74.81°                         Z 45.079    5       63.706         1.6619   32.68                         Y -24.901                                  θ                                    76.76°                         Z 39.978    6     R.sub.y            67.336         1.6619   32.68          R.sub.x            82.918       Y -19.488                                  θ                                    60.27°          K.sub.y            -0.453741    Z 16.092          K.sub.x            -0.466346          AR            4.6317 × 10.sup.-8          BR            1.71366 × 10.sup.-12          AP            -0.308474          BP            -1.22665    7       63.706       Y -24.901                                  θ                                    76.76°                         Z 39.978    8       111.602        1.5092   68.07                         Y -18.553                                  θ                                    74.81°                         Z 45.079    9     R.sub.y            491.360      Y 9.366  θ                                    49.18°          R.sub.x            ∞      Z 33.561          K.sub.y            -23.545228          K.sub.x            0.000000          AR            -3.12497 × 10.sup.-8          BR            3.17327 × 10.sup.-12          AP            -3.99521          BP            -0.577359    10      (display device)                         Y 7.910  θ                                    97.72°                         Z 60.951    (1)  R.sub.y 2/R.sub.x 2 = 0.812    (2) α = 40.82°    Example 5    1       ∞(pupil)                    24.904    2     R.sub.y            93.146         1.4870   70.40          R.sub.x            93.100       Y -2.281 θ                                    -1.71°          K.sub.y            0.164655          K.sub.x            -0.845638          AR            -7.83979 × 10.sup.-8          BR            4.49774 × 10.sup.-10          AP            0.222841          BP            0.223382    3     R.sub.y            463.262        1.4870   70.40          R.sub.x            ∞      Y -21.248                                  θ                                    47.76°          K.sub.y            10.958       Z 17.229          K.sub.x            0.000000          AR            -3.20926 × 10.sup.-10          BR            -7.75816 × 10.sup.-11          AP            -11.4842          BP            -1.18875    4       236.753      Y -20.560                                  θ                                    80.17°                         Z 33.297    5     R.sub.y            60.993       Y -16.708                                  θ                                    53.97°          R.sub.x            93.509       Z 12.262          K.sub.y            -0.417798          K.sub.x            -0.124282          AR            -1.82409 × 10.sup.-9          BR            -2.29964 × 10.sup.-11          AP            5.70288          BP            -1.42015    6       236.753        1.4870   70.40                         Y -20.560                                  θ                                    80.17°                         Z 33.297    7     R.sub.y            463.262      Y -21.248                                  θ                                    47.76°          R.sub.x            ∞      Z 17.229          K.sub.y            10.958          K.sub.x            0.000000          AR            -3.20926 × 10.sup.-10          BR            -7.75816 × 10.sup.-11          AP            -11.4842          BP            -1.18875    8       (display device)                         Y 8.904  θ                                    93.09°                         Z 62.046    (1)  R.sub.y 2/R.sub.x 2 = 1.000    (2) α = 42.24°    Example 6    1       ∞(pupil)                    25.116    2       108.105        1.5779   60.23                         Y 2.027  θ                                    -3.83°    3     R.sub.y            1676.967       1.5779   60.23          R.sub.x            ∞      Y 7.253  θ                                    48.56°          K.sub.y            -1.135218    Z 32.312          K.sub.x            0.000000          AR            -1.8564 × 10.sup.-10          BR            -2.95405 × 10.sup.-13          AP            -8.1079          BP            -2.4482    4       49.089         1.6619   32.68                         Y -25.370                                  θ                                    76.20°                         Z 38.548    5     R.sub.y            97.125         1.6619   32.68          R.sub.x            100.373      Y -13.327                                  θ                                    56.84°          K.sub.y            -0.514166    Z 5.687          K.sub.x            -0.739895          AR            5.54015 × 10.sup.-8          BR            -5.22115 × 10.sup.-12          AP            98.8859          BP            0.121884    6       49.089         1.5779   60.23                         Y -25.370                                  θ                                    76.20°                         Z 38.548    7     R.sub.y            1676.967     Y 7.253  θ                                    48.56°          R.sub.x            ∞      Z 32.312          K.sub.y            -1.135218          K.sub.x            0.000000          AR            -1.8564 × 10.sup.-10          BR            -2.95405 × 10.sup.-13          AP            -8.1079          BP            -2.4482    8       (display device)                         Y 5.841  θ                                    78.81°                         Z 59.335    (1)  R.sub.y /R.sub.x = 0.968    (2) α = 41.44°    Example 7    1       ∞(pupil)                    24.954    2       82.210         1.6524   33.40                         Y -1.588 θ                                    -1.10°    3       27.869         1.6200   60.30                         Y 6.895  θ                                    -12.09°                         Z 28.621    4     R.sub.y            -304.883       1.6200   60.30          R.sub.x            -199.708     Y 20.855 θ                                    50.44°          K.sub.y            -27.32181    Z 25.995          K.sub.x            0.000000          AR            -2.38693 × 10.sup.-8          BR            -4.01613 × 10.sup.-12          AP            0.331362          BP            -0.774091    5     R.sub.y            140.065        1.6200   60.30          R.sub.x            117.775      Y -6.911 θ                                    60.00°          K.sub.y            -2.336694    Z 18.219          K.sub.x            -7.921931          AR            -2.36277 × 10.sup.-8          BR            -1.22629 × 10.sup.-12          AP            0.136585          BP            1.26004    6     R.sub.y            -304.883     Y 20.855 θ                                    50.44°          R.sub.x            -199.708     Z 25.995          K.sub.y            -27.32181          K.sub.x            0.000000          AR            -2.38693 × 10.sup.-8          BR            -4.01613 × 10.sup.-12          AP            0.331362          BP            -0.774091    7       (display device)                         Y 2.249  θ                                    79.24°                         Z 63.702    (1)  R.sub.y 2/R.sub.x 2 = 1.189    (2) α = 39.56°    Example 8    1       ∞(pupil)                    24.280    2       106.771        1.4870   70.40                         Y -5.860 θ                                    -5.48°    3       -43.532                         Y 7.136  θ                                    -1.02°                         Z 31.861    4       -49.540        1.6200   60.30                         Y 4.827  θ                                    -3.99°                         Z 33.709    5     R.sub.y            -344.333       1.6200   60.30          R.sub.x            -221.534     Y 1.7071 θ                                    47.61°          K.sub.y            -29.506325   Z 29.985          K.sub.x            0.000000          AR            -6.62719 × 10.sup.-9          BR            8.7999 × 10.sup.-12          AP            0.3146          BP            -0.608616    6     R.sub.y            134.853        1.6200   60.30          R.sub.x            111.312      Y -10.136                                  θ                                    60.00°          K.sub.y            -2.228243    Z 22.094          K.sub.x            -5.058892          AR            1.03782 × 10.sup.-9          BR            -5.43772 × 10.sup.-13          AP            -4.95485          BP            1.6409    7     R.sub.y            -344.333     Y 17.071 θ                                    47.61°          R.sub.x            -221.534     Z 29.985          K.sub.y            -29.506325          K.sub.x            0.000000          AR            -6.62719 × 10.sup.-9          BR            8.7999 × 10.sup.-12          AP            0.3146          BP            -0.608616    8       (display device)                         Y 2.256  θ                                    77.94°                         Z 64.333    (1)  R.sub.y 2/R.sub.x 2 = 1.211    (2) α = 42.39°    Example 9    1       ∞(pupil)                    23.327    2       104.277        1.6200   60.30                         Y 6.005    -4.77°    3       -977.974       1.7201   46.70                         Y 12.778 θ                                    -3.00°                         Z 26.314    4     R.sub.y            731.548        1.7201   46.70          R.sub.x            ∞      Y 2.779  θ                                    45.59°          K.sub.y            0.000000     Z 38.174          K.sub.x            0.000000          AR            -1.00706 × 10.sup.-8          BR            -3.2973 × 10.sup.-11          AP            -1.9345          BP            -1.41996    5       45.954         1.7550   27.60                         Y -24.307                                  θ                                    74.19°                         Z 39.647    6     R.sub.y            99.662         1.7550   27.60          R.sub.x            114.270      Y -10.489                                  θ                                    53.63°          K.sub.y            -0.894536    Z 8.547          K.sub.x            -0.71734          AR            6.52729 × 10.sup.-8          BR            -3.70088 × 10.sup.-11          AP            0.224738          BP            -0.957649    7       45.954         1.7201   46.70                         Y -24.307                                  θ                                    27.60°                         Z 39.647    8     R.sub.y            731.548      Y 2.779  θ                                    45.59°          R.sub.x            ∞      Z 38.174          K.sub.y            0.000000          K.sub.x            0.000000          AR            -1.00706 × 10.sup.-8          BR            -3.2973 × 10.sup.-11          AP            -1.9345          BP            -1.41996    9       (display device)                         Y 5.982  θ                                    70.67°                         Z 60.426    (1)  R.sub.y 2/R.sub.x 2 = 0.872    (2) α = 44.41°    Example 10    1       ∞(pupil)                    29.657    2       122.705        1.5422   65.21                         Y 11.498 θ                                    -1.01°    3       1482.183       1.5422   65.21                         Y 30.172 θ                                    50.00°                         Z 12.368    4       118.749        1.5422   65.21                         Y -17.459                                  θ                                    69.49°                         Z 17.231    5       1482.183     Y 30.172 θ                                    50.00°                         Z 12.368    6       1540.704                    7.041  1.6200   36.30                         Y 19.919 θ                                    49.92°                         Z 29.590    7       148.781    8       (display device)                         Y 19.920 θ                                    83.32°                         Z 66.180    (1)  R.sub.y 2/R.sub.x 2 = 1    (2) α = 40.00°    __________________________________________________________________________

Although examples in which the optical apparatus according to thepresent invention is applied to an image display apparatus have beendescribed above, it should be noted that the present invention is notnecessarily limited to these examples, and that various modificationsmay be imparted thereto. To arrange the optical apparatus according tothe present invention as a head-mounted image display apparatus (HMD)13, as shown in the sectional view of FIG. 11(a) and the perspectiveview of FIG. 11(b), the HMD 13 is fitted to the observer's head by usinga headband 10, for example, which is attached to the HMD 13. In thisexample of use, the HMD 13 may be arranged such that the second surface2 of the ocular optical system is formed by using a semitransparentmirror (half-mirror) 12, and a liquid crystal shutter 11 is provided infront of the half-mirror 12, thereby enabling an outside world image tobe selectively observed or superimposed on the image of the imagedisplay device 6.

Further, the ocular optical system of the image display apparatusaccording to the present invention can be used as an imaging opticalsystem. For example, as shown in the perspective view of FIG. 12, theocular optical system may be used in a finder optical system F_(i) of acompact camera C_(a) in which a photographic optical system O_(b) andthe finder optical system F_(i) are provided separately in parallel toeach other. FIG. 13 shows an arrangement of an optical system in a casewhere the ocular optical system of the present invention is used as suchan imaging optical system. As illustrated, the ocular optical system DSof the present invention is disposed behind a front lens group GF and anaperture diaphragm D, thereby constituting an objective optical systemL_(t). An image that is formed by the objective optical system L_(t) iserected by a Porro prism P, in which there are four reflections,provided at the observer side of the objective optical system L_(t),thereby enabling an erect image to be observed through an ocular lensO_(c).

As will be clear from the foregoing description, it is possibleaccording to the present invention to provide an image display apparatuswhich has a wide field angle and is extremely small in size and light inweight.

What we claim is:
 1. An image-forming optical system which forms animage of an object,said image-forming optical system comprising at leastone prism member, wherein said prism member has a first surface, asecond surface, and a third surface, said first surface, second surfaceand third surface facing each other across a medium having a refractiveindex (n) larger than 1 (n>1), so that light rays from an object side ofsaid prism member enter said prism member by passing through said firstsurface and are reflected by said second surface and further reflectedby said third surface, and the reflected light rays exit from said prismmember by passing through said second surface, wherein both said secondsurface and said third surface are curved surface configurations, and atleast one of the curved surface configurations is formed from arotationally asymmetric curved surface.
 2. An image-forming opticalsystem according to claim 1, wherein said second surface of said prismmember is formed from a totally reflecting surface so as to have both atransmitting action and a reflecting action.
 3. An image forming opticalsystem according to claim 1, which satisfies the following condition:

    30°<α<70°

where α is an angle formed between said second surface of said prismmember and an optical axis of the light rays from said object side. 4.An image-forming optical system according to any one of claims 1 to 3,wherein said rotationally asymmetric curved surface is formed from aconfiguration having an aberration correcting action to correctdecentration aberrations caused by reflection in said prism member. 5.An image-forming optical system according to claim 4, wherein said thirdsurface is formed from said rotationally asymmetric curved surface. 6.An image-forming optical system according to claim 5, wherein said firstsurface is formed from a spherical surface configuration.
 7. Animage-forming optical system according to claim 4, wherein said secondsurface is formed from a spherical surface configuration.
 8. Animage-forming optical system according to claim 7, wherein said firstsurface is formed from a spherical surface configuration.
 9. Animage-forming optical system according to claim 4, wherein both saidsecond surface and said third surface are formed from rotationallyasymmetric curved surfaces.
 10. An image-forming optical systemaccording to claim 9, wherein said first surface is formed from aspherical surface configuration.
 11. An image-forming optical systemaccording to claim 4, wherein said first surface, said second surfaceand said third surface are all formed from rotationally asymmetriccurved surfaces.
 12. An image-forming optical system according to claim4, wherein said third surface is formed from a curved surfaceconfiguration having a concave surface directed toward said medium. 13.An image-forming optical system according to claim 4, wherein saidsecond surface is formed from a curved surface configuration having aconcave surface directed toward the image.
 14. An image-forming opticalsystem according to claim 4, further comprising a lens disposed closerto the object than said prism member.
 15. An image-forming opticalsystem according to claim 14, wherein said lens is a positive lens. 16.An image-forming optical system according to claim 14, wherein said lensis a negative lens.
 17. An image-forming optical system according toclaim 4, further comprising a lens disposed closer to the image thansaid prism member.
 18. An image-forming optical system according toclaim 4, further comprising an aperture stop,wherein said prism memberis disposed between said aperture stop and said object image.
 19. Animage-forming optical system according to claim 4, wherein a field anglein a horizontal direction of said prism member is different from a fieldangle in a vertical direction thereof.
 20. An image forming opticalsystem according to claim 19, wherein the field angle in the horizontaldirection of said prism member is larger than the field angle in thevertical direction thereof.
 21. A camera apparatus according to claim 4,wherein said image-forming optical system is disposed to perform imageformation.
 22. A camera apparatus according to claim 21, wherein aphotographic optical system and a finder optical system are disposedseparately from each other.
 23. A camera apparatus according to claim22, wherein said image-forming optical system is disposed in said finderoptical system.
 24. A camera apparatus according to claim 23, whereinsaid finder optical system includes, in order from an object sidethereof, said image-forming optical system, an image erecting opticalsystem for erecting the object image formed by said image-formingoptical system, and an ocular optical system for observing said objectimage.
 25. An ocular optical system arranged to lead an image formed onan image plane to an observer's eyeball,said ocular optical systemcomprising at least one prism member, wherein said prism member has afirst surface, a second surface, and a third surface, said firstsurface, second surface and third surface facing each other across amedium having a refractive index (n) larger than 1 (n>1), so that lightrays from said image enter said prism member by passing through saidsecond surface and are reflected by said third surface and furtherreflected by said second surface, and the reflected light rays exit fromsaid prism member by passing through said first surface, wherein bothsaid second surface and said third surface are curved surfaceconfigurations, and at least one of the curved surface configurations isformed from a rotationally asymmetric curved surface.
 26. An ocularoptical system according to claim 25, wherein said second surface ofsaid prism member is formed from a totally reflecting surface so as tohave both a transmitting action and a reflecting action.
 27. An ocularoptical system according to claim 25, which satisfies the followingcondition:

    30°<α<70°

where α is an angle formed between said second surface of said prismmember and an observer's visual axis.
 28. An ocular optical systemaccording to any one of claims 25 to 27, wherein said rotationallyasymmetric curved surface is formed from a configuration having anaberration correcting action to correct decentration aberrations causedby reflection in said prism member.
 29. An ocular optical systemaccording to claim 28, wherein said third surface is formed from saidrotationally asymmetric curved surface.
 30. An ocular optical systemaccording to claim 29, wherein said first surface is formed from aspherical surface configuration.
 31. An ocular optical system accordingto claim 28, wherein said second surface is formed from saidrotationally asymmetric curved surface.
 32. An ocular optical systemaccording to claim 31, wherein said first surface is formed from aspherical surface configuration.
 33. An ocular optical system accordingto claim 28, wherein both said second surface and said third surface areformed from rotationally asymmetric curved surfaces.
 34. An ocularoptical system according to claim 33, wherein said first surface isformed from a spherical surface configuration.
 35. An ocular opticalsystem according to claim 28, wherein said first surface, said secondsurface and said third surface are all formed from rotationallyasymmetric curved surfaces.
 36. An ocular optical system according toclaim 28, wherein said third surface is formed from a curved surfaceconfiguration having a concave surface directed toward said medium. 37.An ocular optical system according to claim 28, wherein said secondsurface is formed from a curved surface configuration having a concavesurface directed toward the image.
 38. An ocular optical systemaccording to claim 28, further comprising a lens disposed closer to theobserver's eyeball than said prism member.
 39. An ocular optical systemaccording to claim 38, wherein said lens is a positive lens.
 40. Anocular optical system according to claim 38, wherein said lens is anegative lens.
 41. An ocular optical system according to claim 28,further comprising a lens disposed closer to the image than said prismmember.
 42. An ocular optical system according to claim 28, wherein afield angle in a horizontal direction of said ocular optical system isdifferent from a field angle in a vertical direction thereof.
 43. Anocular optical system according to claim 42, wherein the field angle inthe horizontal direction of said ocular optical system is larger thanthe field angle in the vertical direction thereof.
 44. In a finderoptical system comprising an objective optical system for forming anobject image; an image erecting optical system for erecting said objectimage; and an ocular optical system for observing said object image;theimprovement which comprises at least one prism member, wherein saidprism member has a first surface disposed on a pupil side of said prismmember and having a transmitting action; a second surface disposed on animage side of said prism member and having both a transmitting actionand a reflecting action; and a third surface having a reflecting action,wherein both said second surface and said third surface are curvedsurface configurations, and at least one of the curved surfaceconfigurations is formed from a rotationally asymmetric curved surface.45. An ocular optical system according to claim 44, wherein said firstsurface of said prism member is formed from a curved surface.
 46. Acamera apparatus according to claim 44 or 45, which has said finderoptical system.
 47. A camera apparatus according to claim 46, which hasa photographic optical system provided separately from said finderoptical system.